Provided is a method for preparing a metal oxide or a metal hydroxide nano thin-film material by a molten salt method, which mainly comprises the following steps: heating a low-melting-point salt to a molten state, adding a substrate into the molten salt before or after melting for reaction; adding a metal source and continuing the reaction for a period of time; removing the substrate, cooling the substrate to a room temperature, cleaning and drying the substrate to obtain the metal oxide or metal hydroxide nano thin-film material; wherein, the mass ratio of the low-melting-point salt to the metal source is 100-1.5:1. The metal oxide and metal hydroxide nano-film materials with various nano-morphologies prepared by the method of the present application have morphologies that can be regulated and controlled by the types and proportions of the low-melting-point salts and metal sources.